N. natrix hunting frogs in water or not?

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N. natrix hunting frogs in water or not?

Postby Berislav Horvatic » Sun Jan 31, 2016 3:44 pm

Regarding the topic viewtopic.php?f=13&t=2399 I have a "theoretical" question.

Someone told me once that Natrix natrix just don't hunt frogs in water, only on dry land, which
might be the reason (or one of the reasons) why they tolerate each other's close presence in water
so calmly, as they indeed seem to do.
Is that true?
Of course, if a Natrix natrix decides to hunt fish, which they also do, it has to do it in water,
obviously. But with their main food they have a simpler (?) choice. My impression is that frogs
are much better/faster swimmers than snakes, so hunting them in water is too demanding to
be attempted at all... and the frogs "know" it, as well as the snakes.
Any facts and/or opinions?
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Re: N. natrix hunting frogs in water or not?

Postby Niklas Ban » Sun Jan 31, 2016 6:19 pm

It is proven wrong, I have no picture, but I have seens Pelophylax lessonae hunted and eaten by Natrix natrix helvetica in an little pond by cologne. If you stay there a while you will observe it too. Even if you google it you find pictures.
I guess that the brain of Natrix is just able to "think" about one thing for example "fleeing-mode" "eating-mode", so if a Natrix know you are there it will decide to flee instead of hunting. If I am right a simple brain as the Natrix or frog brain needs a stimulus to react. If they both lay in water it might be the case that the brian of Natrix just don't get the stimulus to attack the frog, this is why they often seen next to each other.
I have to say, that I just can't explain my whole thoughts in Englisch. :lol:
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Re: N. natrix hunting frogs in water or not?

Postby Berislav Horvatic » Sun Jan 31, 2016 8:09 pm

Niklas Ban wrote:I guess that the brain of Natrix is just able to "think" about one thing for example "fleeing-mode" "eating-mode",
so if a Natrix know you are there it will decide to flee instead of hunting.

No, just suppose I'm not there, or pretending not to be there - keeping quite frozen, not interferring.
I used to do that. The frogs not fleeing, the snakes not fleeing, just lazily moving a little bit from
time to time, ignoring me and each other.

If I am right a simple brain as the Natrix or frog brain needs a stimulus to react. If they both lay in water it might be the case that the brian of Natrix just don't get the stimulus to attack the frog, this is why they often seen next to each other.

Maybe you underestimate snake brains. E.g., vipers feed both on small mammals and birds,
but use two different procedures to catch them, reflecting an at least two-line programme:
(1) If it has fur, bite and release,
(2) if it has feathers, bite and hold.
Pretty smart, don't you think? And they don't LEARN that from their parents, because with
snakes there just isn't any parental care of the offspring, that's an established fact.
Or consider a two-line programme used by the constrictors:
(1) First bite and hold tight,
(2) only if this succeeds, wrap a few coils around and start to constrict.
If they fail securing the prey with a bite, they don't go to step (2), they either retry step (1)
or give up the whole thing.
Male-to-male combats obviously involve a lot more "sofistication" than the above examples.
First, there is quite an elaborate PROCEDURE, and what fascinates me the most is that in
the end the opponents realize who won and who lost, and behave accordingly, both of them.
That's way above anything one might call a "stimulus"... I'd call it understanding.
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Re: N. natrix hunting frogs in water or not?

Postby Alexander Pieh » Mon Feb 01, 2016 1:26 pm

I have seen Natrix n. helvetica feeding on some Salamandra larvae below the surface of a small river without even breathing in between, a Natrix n. natrix spied after I caught it a lot of Bufo bufo tadpoles, a very large N. n. helvetica fed on an adult Bufo bufo on a mountain slope. One Natrix n. natrix hunted Phoxinus phoxinus at night (ca. 10 °C airtemp.).
And of course I have seen several times Natrix n. s.l. (helvetica, persa) chasing Frogs. I haven’t seen a successful hunt, (according to my view I haven´t been at the right time at the right place).
There have been a lot of situations with calm Frog sitting very near to a basking Natrix.
N. n. sl. is for sure a very opportunistic predator.
Frogs and tadpoles on the opposite also know how to react (or not) if there is a predator around. I think sometimes simply snakes can´t realize its “food” (temperature, movement, smell, camouflage).
It would be very interesting to know if the repellence (Alkaloide…) concentration in the skin of Amphibians can be realized by a snake during the hunt and if they distinguish between a more or less “tasty” Frog.
In one situation a N. n. helvetica hatchling vanished after swimming out of my direct sight field. I´m sure that a large P. kl. esculentus didn’t know his right place in the food chain…

Attached a pic:
(Sorry for the rude situation.)
I´m not sure if the Natrix n. helvetica was able to swallow the toad at the end. Any predator would have been able to capture the snake during the process. So it was high risk without the guaranty of success.
...Understanding? I don´t think so. "Instinct" – whatever it is….
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Re: N. natrix hunting frogs in water or not?

Postby Ilian Velikov » Mon Feb 01, 2016 2:32 pm

Regarding frogs and snakes being in a close proximity of each other without the frog fleeing or the snake attacking we could look at other examples of such behavior between other predators and prey. On the African Savannah one could see lions or cheetahs walking about at a few meters from antelope or zebra which wouldn't do much more than keep an eye on them and carry on grazing...Why is that? Why the antelope don't run every time they see a predator? Maybe it has to do with recognizing the predator's mode and conserving energy...? If a frog that lives in a pond where there are predators everywhere, on the bank and on the water surface (snakes, mammals, birds), underwater(fish), in the sky (birds) it would have to spend its whole day and energy just fleeing from them. I think they just take their chances, sometimes they'll just keep still and rely on camouflage and sometimes they'd leap in the water or dive to the bottom. How or if they judge the situation I don't know.
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Re: N. natrix hunting frogs in water or not?

Postby Berislav Horvatic » Mon Feb 01, 2016 8:37 pm

Ilian Velikov wrote:Why the antelope don't run every time they see a predator? Maybe it has to do with recognizing
the predator's mode and conserving energy...?

In case of zebras (or antelopes) and lions, the answer is most probably a yes. After all, lions don't attack
everything that moves around them ten times a day - for most of the time they do just nothing at all, and
zebras seem to know that. They also recognize the signs of alarm - when the lionesses start preparing for
a hunt... It's an easily recognizable behaviour, and zebras react to it accordingly.

Are frogs "intelligent" enough to do the same?
(I expect no straight answer to that at all. I think that would surpass all... you name it.)

But that was not my point in asking the original question. Unlike lions, Natrix natrix have two scenarios
offered for catching frogs - on dry land or in water. If the latter is much much more difficult, they might
have given it up (almost) altogether, and the frogs know it and count on that... Therefore my question:
Do the grass snakes attempt it in water at all? (The answer was a yes.) If they do, how often? Is it very
exceptional (enough so that the frogs can take the risk...), or quite common (in which case frogs make
a "terrible mistake"...)?
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Re: N. natrix hunting frogs in water or not?

Postby Niklas Ban » Mon Feb 01, 2016 9:19 pm

Berislav Horvatic wrote:Maybe you underestimate snake brains.

I totally not. But there are much smarter snakes than Natrix.
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Re: N. natrix hunting frogs in water or not?

Postby Berislav Horvatic » Mon Feb 01, 2016 10:06 pm

Niklas Ban wrote:
Berislav Horvatic wrote:Maybe you underestimate snake brains.

I totally not. But there are much smarter snakes than Natrix.

Of course, Malpolon, Coronella, king cobra, ... But, mind you, that is not an issue at all here & now.
Certainly deserves a new "thread", at least in the "Theoretical section", and a few dozens of scientific
papers to support it, either extant or future ones...
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Re: N. natrix hunting frogs in water or not?

Postby Robert Madl » Tue Feb 02, 2016 11:52 pm

In this context I remember a frog hunting Natrix natrix persa, I've seen in Cres, doing both...
https://youtu.be/r_0lI210eRQ
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Re: N. natrix hunting frogs in water or not?

Postby Berislav Horvatic » Wed Feb 03, 2016 12:43 am

I meant hunting in deep water, not like this. But the movie itself is very nice.
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